This proposal seeks to investigate a novel biologic mechanism behind the pathogenesis of craniosynostosis. Craniosynostosis is a debilitating pediatric condition in which adjacent cranial bones become prematurely fused. This pediatric abnormality can lead to abnormal skull and facial shapes, blindness, seizures and cognitive deficits. Craniosynostosis is currently treated surgically. Therefore even with appropriately early diagnosis, severely affected patients suffer high morbidity. Previous studies demonstrated that craniosynostosis is associated with genetic mutations in Fibroblast Growth Factor (FGF) Receptors, Twist, TCF12, Msx2, Efnb1 and Gli3; and that the pathogenesis of craniosynostosis can include defective boundary formation, cell lineage commitment, proliferation and/or apoptosis of cranial bone and suture cells. Despite these important advancements, a pharmaceutical treatment option for craniosynostosis has not yet been realized. We recently reported that the tissue non-specific alkaline phosphatase (TNAP/Alpl) null mouse model of hypophosphatasia exhibits craniosynostosis, an abnormal craniofacial skeletal shape, and abnormal cranial progenitor cell proliferation and osteoblast differentiation. These facts indicate that TNAP has a previously unrecognized and essential function regulating cranial progenitor cell development that influences craniosynostosis. Based upon these findings and upon known enzymatic activities of TNAP, we hypothesize that abnormal inorganic pyrophosphate metabolism due to unbalanced expression of TNAP (pyrophosphate hydrolyzing enzyme) and ENPP1 (pyrophosphate-generating enzyme) causes hypophosphatasia-associated craniosynostosis. Additionally, we also hypothesize that abnormalities in this pathway contribute to FGFR- associated craniosynostosis. Here we propose to utilize genetic and pharmacologic approaches to define mechanisms by which ENPP1 and TNAP mediate hypophosphatasia-associated and FGFR-associated forms of craniosynostosis. Of clinical significance, our data suggests that enzyme replacement strategies currently used to treat hypophosphatasia patients could be used to prevent and/or diminish the severity of craniosynostosis. These treatments could decrease craniosynostosis severity and normalize craniofacial shape defects to a greater extent than surgery alone, greatly improving patient quality of life.